One long felt need in the contact lens industry is to provide contact lenses which are comfortable for users to wear. Generally, the problems that contact lens users complain of most are initial discomfort (i.e., immediately after lens insertion), discomfort associated with dry-eye conditions and/or working or living in dry environments, and end-of-day comfort. Several approaches have been developed to address the comfort issue.
For example, soft contact lenses have been developed to alleviate some of the problems, such as initial discomfort, relatively long periods of adaptation (a week or two) required for a patient to become accustomed to them, and/or improper fit (lenses become dislodged and/or are very uncomfortable). This is due, not only, to their relatively soft surfaces, but also to their pliability, which permits them to modify their shape somewhat with different eyes.
One of the widely used approaches to improve ocular comfort with contact lenses is to apply directly eye drops of an ocular lubricant into the wearer's eye while the lens is being worn, in order to provide some relief to some extent, e.g., the initial discomfort of wearers, discomfort suffering from dry-eye effects, or end-of-day discomfort. However, there are unavoidable disadvantages with this approach. For example, eye drops are typically applied only after a lens wearer is already suffering discomfort and as such do not prevent the discomfort from occurring. Furthermore, a user needs to easily and conveniently access eye drops to ease the discomfort and therefore has to carry a bottle of eye drops with him/her. This adds cost and inconvenience to the lens wearers.
Recently, surfactants, lubricants or other additives are added in the lens packaging solution to ease to some extent initial discomfort and other symptoms (see, for example, U.S. Pat. Nos. 5,882,687, 5,942,558, 6,348,507, 6,440,366, 6,531,432, and 6,699,435; and Published PCT Patent Applications WO9720019 and WO2006/088758). However, although such approach may alleviate, to some extent, some forms but not all forms of discomfort, especially the end-of-day comfort, dry-eye symptoms and/or contact lens induced dry-eye symptoms.
In addition, leachable lubricants are incorporated in lens formulations for making contact lenses to alleviate some discomfort symptoms (see for example, U.S. Pat. Nos. 6,822,016 and 6,367,929, U.S. Patent Application Publication No. US 2006/0251696 A1). Although the methods disclosed in the above patents and patent application may alleviate some discomfort symptoms to some extent, not all symptoms can be removed and/or reduced.
Therefore, there exists a need for hydrogel soft contact lenses which not only have initial insertion comfort but also are comfortable to wear for more than about 6 hours.